I did my PhD research on slaking rocks or soft sedimentary rocks, respectively. During my literature research in the beginning of my PhD project it was pretty obvious that there is no general defintion of the terms "soft rock", "weak rock" etc.
There are two fundamental views. On the one hand there are the (classic) defintions with respect to the strength of the rocks on the other hand there are defintions relating to the slaking behaviour of rock.
Even in the very recent book "Soft Rock Mechanics and Engineering" most of the reseachers find it necessary to define the term "soft rock" and how it is used in the following chapters indicating that there are still lots of open questions regarding a general definition of this/these group of geomaterial.
What is your opinion on the definition on the term "soft rock", "weak rock", "slaking rock" etc.?
Hi Christian Ungewitter
I graduate in mining engineering and in my opinion, "weak rock" is suitable
Cordially,
Rashiddel
Alireza Rashiddel
Thank you for your reply.
Aside from the term to use I would like to discuss a general defintion like the one of Nickmann in PhD "Abgrenzung und Klassifizierung veränderlich fester Gesteine unter ingenieurgeologischen Aspekten" (in German).
According to her weak rocks "tend to disintegrate within a short time period (days to several years) when being exposed to water and/or climatic changes. In this case weak rocks can show an extremely varying behaviour from spontaneous decay into small fractions (aggregates or grains) shortly after water supply, to slow degradation into aggregates over months to years. This loss of strength is not reversible under real conditions."
Building on some of the previous posts, in my mind "weak rock" refers to the rock's strength. Typically, a boundary strength value will be specified to separate "weak" from "strong" for a given context.
"Soft rock" refers to how a rock responds to weathering, or how abradable the rock is (there tends to be a correlation, but they are different processes). A rock that quickly weathers is "soft." Likewise, a rock that is readily abraded, for example when it forms a stream bed, is "soft." Often, but not always, these "soft" rocks will exhibit slaking behavior when they are cycled through wetting and drying. It is a specific form of disintegration in response to weathering and is associated with clay minerals. Slaking-like behavior can also result from freezing and thawing or the growth of precipitates, like salt.
Low strength, readily weathered/abraded, and prone to slaking are often attributes that are found together (e.g. a claystone). Likewise, high strength, slow to weather, and not being prone to slaking are often found together (e.g. a quartzite). However, there are exceptions. For example, some sandstones can be relatively strong, but weather relatively quickly without exhibiting slaking behavior.
Matthew Mabey
Your division between weak rock and soft is a very interesting one. I think that this is a sound approach for a more precise definition and distinction between soft rock and weak rock.
There are several definitions enumerated in classic Geological/Civil Text books. Most of them are having qualitative inputs and are fairly good to use while understanding or conveying something about weak rocks. Nonetheless, for a practical use range/limits/categories can be used to be more on quantitative and clearer side. Well, as due to varying composition based on constituents and other conditions, there would always be certain subjective/qualitative interpretation.
Dear Christian,
I work on weak rocks for at least 5 years. the main classification of weak rocks is experimental and depends on geoengineers' experiences. So, it is required experiences to understand the behavior of the materials. nevertheless, these articles might help:
Article An empirical classification method for South Pars marls by S...
Article Geotechnical characteristics and empirical geo-engineering r...
Bests,
- Badges
- Science topic
- Similar topics
- Filing